diff --git a/four.rs b/four.rs
new file mode 100644
index 0000000..dbff933
--- /dev/null
+++ b/four.rs
@@ -0,0 +1,27 @@
+fn main() {
+    let buf = std::fs::read_to_string("four.txt").unwrap();
+    let mut count = 0u32;
+    for line in buf.lines() {
+        let (first, last) = line.split_once(',').unwrap();
+        let (first_lower, first_upper) = first
+            .split_once('-')
+            .map(|(a, b)| (a.parse::<u32>().unwrap(), b.parse::<u32>().unwrap()))
+            .unwrap();
+        let (last_lower, last_upper) = last
+            .split_once('-')
+            .map(|(a, b)| (a.parse::<u32>().unwrap(), b.parse::<u32>().unwrap()))
+            .unwrap();
+
+        if contains(first_lower, first_upper, last_lower, last_upper)
+            || contains(last_lower, last_upper, first_lower, first_upper)
+        {
+            count += 1;
+        }
+    }
+
+    println!("{}", count);
+}
+
+fn contains(a: u32, b: u32, c: u32, d: u32) -> bool {
+    return (a..=b).contains(&c) && (a..=b).contains(&d);
+}
diff --git a/four.txt b/four.txt
new file mode 100644
index 0000000..cb68f6a
--- /dev/null
+++ b/four.txt
@@ -0,0 +1,1000 @@
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